1. Field of the Invention
The present invention relates to a display device in which a plurality of self-emitting pixels are arranged, for example, a self light emitting type display device in which organic EL (electroluminescent) elements are arranged in a matrix pattern as light emitting elements, and particularly to a self light emitting type display device which can correct variations in characteristics of the self-emitting elements, a driver IC which drives lighting of the self-emitting elements, and the like.
2. Description of the Related Art
A display employing a display panel which is constructed by arranging light emitting elements in a matrix pattern has been developed widely. As the light emitting element employed in such display panel, an organic EL element in which an organic material is employed in a light emitting layer has attracted attention, and a display of a self-emitting type in which the organic EL elements are arranged in a matrix pattern has been commercialized partly. This is because of a background that by employing, in a light emission functional layer constituting an EL element, an organic compound which enables an excellent light emission characteristic to be expected, progress in a high efficiency and a long life by which an EL element can be fit for practical use has been made.
As a display device employing the above-mentioned organic EL elements, a passive matrix type display device in which EL elements are simply arranged in a matrix pattern and an active matrix type display device in which respective active elements for example constituted by TFTs (thin film transistors) are added to respective EL elements arranged in a matrix pattern have been proposed.
In the former passive matrix type display device, respective organic EL layers as light emitting pixels are formed at respective crossing positions between first electrode lines arranged in a striped pattern and second electrode lines which are arranged in a striped pattern so as to cross the first electrode lines at right angles. This passive matrix type display device can be provided as a relatively simple structure. On the other hand, in the latter active matrix type display device, although the respective active elements constituted by the above-mentioned TFTs have to be provided for respective pixels, since a momentary intensity of an EL element as a light emitting pixel can be reduced, the lives of the light emitting pixels can be prolonged. Further, the active matrix typed is play device has an advantage such as a less crosstalk light emission between pixels and the like, thereby being suitable for a large screen display and a high-precision display.
In any case in which either one of the above-described type display devices is utilized, this type of self-emitting element typified by an organic EL element has a characteristic that the element emits light at an intensity approximately proportional to the drive current supplied thereto. However, there is a problem that variations in light emission intensities with respect to the drive current occur among respective light emitting elements. Meanwhile, variations in driver ICs which drive lighting of respective light emitting elements occur as a matter of the fabrication thereof. Further, in the active matrix type display device, variations in the above-mentioned TFTs each of which is formed for each pixel unit occur as a matter of the fabrications thereof. Thus, there is a problem that it is difficult to make intensity characteristics on a display screen uniform.
Recently, a display panel which realizes full color display employing as subpixels respective EL elements which emit lights of respective R (red), G (green), and B (blue) colors has been developed. In this case, there is a problem that light emission efficiencies with respect to forward voltages of the respective colors of light emitting elements are different, and it is necessary to adjust these light emission intensities in advance in order to adjust color (white) balance.
In the above-described display devices, in order to correct variations in current vs. intensity of respective light emitting elements, variations in driver ICs, and the like before the product is shipped, and further in order to adjust white balance among respective subpixels, work of adjusting respective drive current values outputted from respective driver ICs has been done. Actual conditions of such adjustment work and one example of adjustment method are disclosed in Japanese Patent Application Laid-Open No. Hei 114-282420 (paragraphs 0014 to 0024 and FIGS. 1 to 5) shown below.
The work for adjusting drive current values in the driver ICs that is done before the product is shipped is executed in a state of semi-finished products of a display device for example shown in FIG. 1. That is, in FIG. 1, reference numeral 1 designates a self-emitting module, and this self-emitting module 1 is composed of a display panel 2, an FPC (flexible printed circuit board) 3, a connector 4, and a driver IC 5 loaded on the FPC 3.
In the display panel 2 constituting the self-emitting module 1, although not specifically shown in the drawing, a large number of self-emitting elements, for example, organic EL elements, are arranged in a matrix pattern, and thus images can be reproduced in a light emitting state. One end of the FPC 3 is connected with an end edge of the panel 2, for example, by means of thermocompression bonding and the like, and the other end of the FPC 3 is connected with the connector 4 so as to be connected via the connector 4 with a main body substrate 6 which will be described later.
In the driver IC 5 loaded on the FPC 3, mixedly loaded are an anode driver and a cathode driver for selectively driving light emission of the light emitting elements arranged on the display panel 2, constant current sources which supply constant current to respective EL elements arranged on the display panel 2, and the like. The driver IC 5 is mutually connected on a way on the FPC 3 from the connector 4 to the display panel 2.
In the main body substrate 6, loaded are a voltage boosting circuit 7 for example by means of a DC/DC converter, a control CPU 8 which controls the driver IC 5 in the self-emitting module 1 side and which performs data transmission and the like, an intensity setting circuit 9 which can set current values of the respective constant current sources loaded in the driver IC 5, and the like.
As disclosed in Japanese Patent Application Laid-Open No. Hei 11-282420,in order to implement the work of adjusting respective drive current values for adjusting variations in intensities of respective light emitting elements or white balance, in the structure of a conventional display device shown in FIG. 1, since the intensity setting circuit 9 is loaded in the main body substrate 6 side, the adjustment work cannot be implemented unless the self-emitting module 1 is connected with the main body substrate 6 side via the connector 4. Thus, once connecting the self-emitting module 1 with the main body substrate 6 side via the connector 4 and measuring intensities of the display panel 2 in this state prevents fabrication work from being efficient, resulting in a primary factor of increasing the fabrication cost.
That is, in the sense that the fabrication control has to be efficient, it is desired that the intensities of respective light emitting elements can be adjusted, that is, that respective current values supplied from the driver IC 5 can be adjusted in a state in which the module 1 is an individual body before the self-emitting module 1 is connected with the main body substrate 6 side.